How can we have Viva Engage communities that are both dynamic and users can join?

We want to have Viva Engage communities where employees are dynamically assigned: e.g. if you are a member of Business Unit A you get added to the Viva Engage Community for Business Unit A. If you change jobs to Business Unit B you would automatically be added to the Viva Engage community for Business Unit B.

However in addition to dynamic membership we also want people to be able to join the communities manually. e.g. I'm a member of Business Unit B, but I'd like to have the option of joining the Community for Business Unit A just to see what's happening.

Is it possible to have Communities that have dynamic membership but also the option to join as well even if you don't have the necessary attributes?